According to the Wikipedia article on Venera-D,
A lander, based on the Venera design, is also planned, capable of surviving for a long duration on the planet's surface.
The surface of Venus has temperatures of 462°C and pressures of 9.2 MPa. How can any useful payload function for more than a couple of hours in such conditions? In the near-vacuum of space, radiators can be used to get rid of excess heat, but on Venus, the atmosphere would just radiate back, so that wouldn't work. The only solution I can envisions is a giant, powerful, active refrigerator — and that would only address one of the problems. I suppose one would not only need to cool down the instruments, but also external components such as solar panels (if applicable). On the plus side, one should be able to simulate Venus conditions in a lab somewhat accurately.
Have any payloads been demonstrated (in a lab) to function for a longer time in conditions similar to the Venus surface, using active cooling with a feasible power budget? By a longer time, I mean long enough so that mission control can interact with the spacecraft, decide what to look for based on initial results, etc.; so let's say at least one month.
Similar question: What material properties would be necessary to shield a lander from the environment of the Venusian surface?. The other question focusses on materials, whereas I specifically ask if it has been demonstrated in a lab, considering all aspects.